This invention relates to a process for producing fine patterns using a photosensitive composition excellent in developing properties for an alkaline aqueous solution and forming positive images. More in detail, this invention relates to a process for producing fine patterns using a photosensitive composition having high sensitivity to ultraviolet light, high resolving power and high resistance to etching.
With a rapid progress in the semiconductor industry in recent years, there has been required improvement in performance and properties in wide range for resist materials used for pattern formation. In order to meet such a requirement, there have been provided practically various kinds of photosensitive compositions, which have many advantages as well as disadvantages, respectively.
A typical fine pattern making technique having been employed in the field of semiconductor integrated circuits is ultraviolet lithography using a photoresist. The ultraviolet lithography is a very effective means for producing a large number of semiconductor integrated circuits in a short time.
As to resist materials used in the ultraviolet lithography, a typical negative type photoresist is a composition comprising a cyclized rubber and an aromatic azide compound. The cyclized rubber includes polybutadiene, polyisoprene, and the like and is used by adjusting the molecular weight, the degree of dispersion, and the like. The aromatic azide compound includes, for example, azidobenzal ketones such as 2,6-bis(4'-azidobenzal)-4-methylcyclohexanone, 2,6-bis(4'-azidobenzal)-cyclohexanone, etc. In the case of the negative type photoresist obtained by combining the cyclized rubber and the aromatic azide compound, a developing solution used at the time of development for dissolving uncured portions also swells cured portions of resist, which results in causing blisters and meandering in the resist. The swelling of the resist per se by the developing solution seems to be a main factor for lowering the degree of resolution. Therefore, it is impossible at present time to form fine patterns having a width of 0.5 .mu.m to 0.2 .mu.m with high precision by using the composition comprising a cyclized rubber and an aromatic azide compound.
On the other hand, a typical positive type photoresist is a photoresist composition comprising a novolac resin and a quinone diazide compound. The novolac resin includes a phenol novolac resin, a cresol novolac resin, etc. The quinone diazide compound used as photosensitizer includes o-naphthoquinonediazide, etc. Positive type photoresists are generally good in the degree of resolution. This is because the base resin is an organic material such as a novolac resin and the developing solution is an alkaline aqueous solution, so that the resin portion is not swelled at the time of development and only the portion exposed to ultraviolet light is dissolved.
As to etching of a substrate using a resist as mask, there are wet etching and dry etching. Wet etching has been used widely but there is a limitation thereto considering precision of fine patterns and easy peeling of resist at the time of side etching or wet etching.
Considering the above-mentioned points with regards to photoresist materials, cyclized rubber series negative type photoresists are good in resistance to dry etching, but since they are low in the degree of resolution as mentioned above, it is difficult to use them for producing fine patterns.
On the other hand, phenol resin series positive type photoresists are good in the degree of resolution and resistance to etching and are characterized by the positive type.
As to the light source, Japanese Patent Appln Kokai (Laid-Open) No. 162744/81 discloses the use of far ultraviolet light, which requires special apparatus and cannot be used generally.
Further, Japanese Patent Appln Kokoku (Post-Exam Publn) Nos. 22082/70 and 34902/78 disclose that a mixture of a novolac resin or the like and an azide compound is useful as photosensitive resin composition. But these references are quite silent on resistance to etching of such a photosensitive resin composition.